Replace more ObserverList with base::ObserverList.

ui/base/models/tree_node_model.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_BASE_MODELS_TREE_NODE_MODEL_H_
 #define UI_BASE_MODELS_TREE_NODE_MODEL_H_
 
 #include <algorithm>
 #include <vector>
 
@@ skipping 274 matching lines @@
 
   void SetTitle(TreeModelNode* node,
                 const base::string16& title) override {
     DCHECK(node);
     AsNode(node)->SetTitle(title);
     NotifyObserverTreeNodeChanged(node);
   }
 
  private:
   // The observers.
-  ObserverList<TreeModelObserver> observer_list_;
+  base::ObserverList<TreeModelObserver> observer_list_;
 
   // The root.
   scoped_ptr<NodeType> root_;
 
   DISALLOW_COPY_AND_ASSIGN(TreeNodeModel);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_MODELS_TREE_NODE_MODEL_H_